An adaptation/improvement on http://www.thingiverse.com/thing:53301

for my K40 cheap Chinese laser. This one is modified:

1. Clears the hinge/lips on my door (mine has a folded metal flange that tried to dislocate the original)
2. Steps back behind the mirror
3. Has a positive stop and a setscrew for angle, and has a spot for a ball-point-pen-spring instead of an external spring.

Like the other one, when you close the door, this lifts out of the way of the burning beam. Remember to hold it up if you're testing with the door open (you can see that I put binder clip on it if I'm aligning the mirrors)! I've also added (not pictured) an aluminum plate to protect the laser diode from the BFLaser in case I fire it without moving the arm out of the way.

Oh, you want to download, separate, and print the "NoCase" file -- the "Case" file has a lot of blocks that I used to design it (eg a block for where the lid contacts the arm, a block for the plane the laser should be at, and a "keepout" area where the arm has to make a bend to not hit the mirror when it homes).

The laser is a cheap 6mm pointer module (http://amzn.to/1hP4OoM),

You can see how it's laid out in my machine (the big "target" has a ridge that indicates where the laser should be).

There's a small pocket in the arm and the hinge to accept a ball-point pen spring for a positive position when opened (you might need to file the arm/hinge just a bit so the action is smooth). There's also a 3mm hole for a setscrew if you nee to adjust the arm angle (since I made it for my machine, I don't ;)

On my K40 unit, the L bend for the door this mounts to was not level/straight with the bed; a little finagling with a pair of vise-grips fixed that...

No support is needed once you find which way to lay each piece -- the arm and the hinge both have flat sides, and my 3d printer didn't have a problem printing the post in the arm since it doesn't stick out very far.

Remember to lift the arm out of the way if you're firing with the door open!